1. Field of the Invention
The present invention relates to an inspection apparatus, a coordination detection apparatus, a coordination detection method and a wavefront aberration correction method.
2. Description of Related Art
Published Japanese Translation of PCT International Publication for Patent Application, No. 2002-536696 discloses a method for performing a deconvolution operation on data captured by a scanned probe microscope. A point spread function is used in the deconvolution operation. By using the point spread function, it is possible to prevent diffraction of a lens, aberration of the lens and the like from influencing an image.
In recent years, Extremely Ultraviolet Lithography (EUVL) having a wavelength of 13.5 nm has been developed in order to achieve miniaturization of semiconductor patterns. Therefore, an actinic inspection apparatus that uses 13.5 nm Extremely Ultraviolet (EUV) light as illumination light has been developed. The optical system of the EUV light uses a multi-layer film reflection optical system having a reflection surface on which a multi-layer film is formed. In a light collecting optical system, for example, a concave mirror has been used in place of a lens.
In the inspection apparatus using the EUV light, in order to inspect fine patterns or the like, observation at a high magnification and high numerical aperture (NA) is desired. However, an aberration occurs due to the occurrence of a positional error or a manufacturing error of the mirror with the multi-layer film. The observed image is blurred due to the aberration. In order to reduce the occurrences of such an aberration, high-accuracy mirror polishing is required, which causes an increase in the manufacturing cost. Further, in order to secure a resolution of 100 nm or smaller in magnifying observation using the EUV multi-layer film reflector, it is required to suppress wavefront aberration and to polish the reflection surface with extremely high accuracy.
Further, when the multi-layer reflection optical system in which the working distance is about 20 mm or larger and NA is above 0.2 to enable an arrangement of various optical components is used, it is difficult to manufacture such a multi-layer reflection optical system since the mirror diameter is large. That is, when the large-sized curved mirror is used, it is difficult to process such a curved mirror with high accuracy. This causes blurring in the optical image due to wavefront aberration.
The present invention has been made in view of the above circumstances and aims to provide an inspection apparatus and a wavefront aberration correction method capable of suppressing fuzziness of an optical image due to wavefront aberration.
Another problem is described hereinbelow. When a defect mitigation is carried out in the EUVL, a pattern of an absorber is formed to cover the defect. It is therefore possible to hide the defect by the pattern of the absorber, whereby it is possible to prevent the defect from being transferred into a wafer.
As described above, in order to carry out the defect mitigation, after an EUV mask blanks is inspected, the pattern of the absorber of the EUV mask is formed in the blanks by an EB drawing apparatus. In order to cover the defect with the pattern of the absorber, it is required to detect the defect with high position accuracy. Accordingly, it is required in the defect inspection apparatus to carry out the alignment with high position accuracy.
Typically, an alignment mark (fiducial mark) is used in the alignment of the mask. For example, the fiducial mark is detected with high position accuracy to inspect the defect. By using the fiducial mark as reference coordinates, the coordinates of the defect may be detected with high position accuracy.
Typically, a cross pattern is used as the fiducial mark (Japanese Unexamined Patent Application Publication No. 2005-83795). The cross pattern is formed, for example, by forming a groove. It is technically required to accurately detect the fiducial mark with high repeatability in order to increase the accuracy of the position of the coordinates of the defect. When an image is blurred, however, the fiducial mark may not be detected with high detection accuracy.
The present invention has been made in view of the above circumstances and aims to provide a coordinate detection apparatus, an inspection apparatus, and a coordinate detection method capable of accurately detecting coordinates.